The present invention relates to a printing switching apparatus, arranged in a sheet-fed rotary press with a reversing mechanism capable of performing both single-sided printing and perfecting printing, for adjusting circumferential phases of upstream and downstream cylinders with respect to a reversing cylinder in switching between single-sided printing and perfecting printing.
Various sheet-fed rotary presses each capable of performing single-sided printing and perfecting printing have been proposed and put into practice along with a variety of printing techniques. An example of such a rotary press is disclosed in Japanese Patent Laid-Open No. 4-146149 in which a transfer cylinder, a cylinder having a diameter twice that of the transfer cylinder, and a reversing cylinder are arranged between an upstream cylinder and a downstream cylinder along a paper convey direction. This rotary press will be described below.
FIG. 7 shows a cylinder arrangement in a single-sided printing state in the sheet-fed rotary press with a reversing mechanism, disclosed in this prior art. FIG. 8 shows a cylinder arrangement in a perfecting printing state in this press. Referring to FIGS. 7 and 8, a first impression cylinder 5 having a gripper unit 4 having grippers 2 and gripper pads 3 axially and parallelly arranged with the grippers 2 in a gap of the first impression cylinder 5 is pressed against a blanket cylinder 1 pressed against a plate cylinder (not shown) mounted with a plate. A second impression cylinder 10 having a gripper unit 9 having grippers 7 and gripper pads 8 axially and parallelly arranged with the grippers 7 in a gap of the second impression cylinder 10 is pressed against a blanket cylinder 6 pressed against a plate cylinder (not shown) mounted with a plate.
A transfer cylinder 11, a cylinder 12 having a diameter twice that of the transfer cylinder 11, and a reversing cylinder 13 are arranged to be pressed against each other between the first and second impression cylinders 5 and 10. A gripper unit 16 having grippers 14 and gripper pads 15 is axially arranged parallel to each other in a gap of the transfer cylinder 11.
Gripper units 19 and 20 respectively having grippers 17 and gripper pads 18 are axially and parallelly arranged in the gaps at positions which divide the circumference of the cylinder 12 into halves. The gripper units 19 and 20 are circumferentially movable.
Suckers 21 and 22 are connected to a blower through rotary valves or the like at positions which divide the circumference of the cylinder 12 into halves and are circumferentially phase-shifted from the gripper units 19 and 20 by about 45.degree.. A gripper unit 25 having grippers 23 and gripper pads 24 and a gripper unit 28 having grippers 26 and gripper pads 27 are arranged in gaps of the reversing cylinder 13 at positions slightly phase-shifted in the circumferential direction of the reversing cylinder 13.
FIG. 9 shows the main part of a conventional printing switching apparatus. Referring to FIG. 9, a gear 32 circumferentially fixed with a key 31 is mounted on an end shaft 30 of the reversing cylinder 13 such that the axial movement of the fixed gear 32 is regulated by an end plate 33. A rotary gear 34 is pivotally mounted on the stepped portion of the fixed gear 32.
Reference numerals 35 denote a plurality of bolts 35 extending through holes 36a and 37a and holes 32a corresponding to the holes 36a and 37a. The holes 36a and 37a are formed at almost equal angular intervals of the circumferences of discs 36 and 37 formed to sandwich the fixed gear 32. The holes 32a are formed in the fixed gear 32. Nuts 38 are threadably engaged with the distal end threaded portions of the bolts 35. A friction plate 39 is interposed between the rotary gear 34 and the disc 37. A leaf spring 40 having an elastic force is interposed between the fixed gear 32 and the disc 36.
On the other hand, a reduction gear group 43 is coupled to the motor shaft of a motor 42 arranged on a frame 41 side. A shaft 44a integral with a last gear 44 of the reduction gear group 43 is threadably engaged with a screw hole 41a of a frame 41. In the illustrated state, the fixed gear 32 and the rotary gear 34 are set stationary. When the motor 42 is rotated in this state, the reduction gear group 43 is rotated to feed the shaft 44a of the gear 44 by the function of the screw hole 41a, thereby urging the disc 36. The stationary state between the fixed gear 32 and the rotary gear 34 is released because the rotary gear 34 is locked by the frictional force of the frictional plate 39.
Each cylinder is driven and coupled in accordance with the meshed state of a cylinder gear at the corresponding shaft end portion and the stationary state between the fixed and rotary gears 32 and 34. At the same time, the fixed gear 32 of the reversing cylinder 13 is meshed with the cylinder gear of the second impression cylinder 10, and the rotary gear 34 of the reversing cylinder 13 is meshed with the cylinder gear of the cylinder 12. For this reason, the stationary state between the fixed and rotary gears 32 and 34 of the reversing cylinder 13 is released. As a result, coupling between the upstream cylinder group including the reversing cylinder 12 and the downstream cylinder group including the reversing cylinder 13 is released.
With the above structure, in the single-sided printing mode shown in FIG. 7, when each cylinder is rotated, a paper sheet 29 printed between the blanket cylinder 1 and the first impression cylinder 5 is gripped between the gripper units 4 and 16 and then between the gripper unit 16 and the gripper units 19 and 20. The paper sheet 29 is wound on the upper-side surface of the cylinder 12.
When the leading end of the paper sheet 29 reaches a contact point between the cylinders 12 and 13, the paper sheet 29 is gripped from the gripper units 19 and 20 to the gripper unit 25 and is wound on the lower-side surface. The paper sheet 29 is then gripped to the gripper unit 9 of the second impression cylinder 10 and then conveyed. When the paper sheet 29 passes between the blanket cylinder 6 and the second impression cylinder 10, printing is performed on the previously printed surface.
When such single-sided printing is to be switched to perfecting printing, the motor 42 is rotated to move the gear shaft 44a of the gear 44 in accordance with the meshed state of the reduction gear group 43 and the screwing action of the screw hole 41a, thereby urging the disc 36. Therefore, the stationary state between the fixed gear 32 and the rotary gear 34 is released.
As shown in FIG. 8, the upstream cylinder group including the rotary gear 34 is rotated by the vertical length of the paper sheet 29 until the sucker 21 opposes the grippers 28, and the motor 42 is rotated in the reverse direction. In this case, the locked state between the rotary gear and the frictional plate 39 is released to set the fixed gear 32 and the rotary gear 34 in the stationary state.
Upon completion of this preparation, when perfecting printing is started, as shown in FIG. 8, the paper sheet 29 whose upper surface has been printed between the blanket cylinder 1 and the impression cylinder 5 is gripped between the gripper units 4 and 16 and then between the gripper unit 16 and the gripper units 19 and 20. As a result, the paper sheet 29 is wound on the upper-side surface of the cylinder 12.
In this state, when all the cylinders are continuously rotated, the leading end of the paper sheet 29 passes through the contact point between the cylinders 12 and 13. When the trailing end of the paper sheet 29 reaches the contact point between the cylinders 12 and 13, the sucker 21 draws this trailing end of the paper sheet 29. At the same time, the gripper unit 20 is opened to release the leading end of the paper sheet 29. The gripper unit 28 having the grippers 26 whose distal ends face in a direction to grip the paper sheet grips the trailing end of the paper sheet 29, thereby reversing and conveying the paper sheet 29.
During conveyance, the paper sheet 29 is gripped from the reversing gripper unit 28 to the gripper unit 25 facing in a direction to grip the paper sheet and then gripped to the gripper unit 9 of the second impression cylinder 10. The lower surface of the paper sheet 29 is printed while passing between the blanket cylinder 6 and the second impression cylinder 10, thereby performing perfecting printing.
The printing switching apparatus in the conventional sheet-fed rotary press with a reversing mechanism requires a large force enough to lock the fixed gear 32 and the rotary gear 34 without any slip. To release this locked state with a small force, the reduction gear group 43 and the like must be arranged between an operation member and the disc 36. This mechanism tends to be worn to cause a failure.